1. Field of the Invention
The present invention relates to a broadcast receiving system for receiving a broadcast, and more particularly, to a broadcast receiving system capable of receiving an irregular broadcast such as a special newscast while keeping usual power consumption low. The present invention also relates to a relay apparatus and a mobile station that are used in the broadcast receiving system, a program for controlling the broadcast receiving system, and a broadcast receiving method.
2. Description of the Related Art
Mobile stations capable of receiving television, radio, and other broadcasts have come into wide use in recent years. Mobile stations are predicted to serve in future one of means for receiving broadcasts including emergency information from digital terrestrial broadcasting (hereinafter abbreviated as DTB). For instance, DTB can be used as away to deliver emergency alert information to a user of the mobile station when a disaster strikes an area where the user is. The emergency information can be displayed on a display screen of the mobile station among other received broadcast contents if the mobile station is always in a state capable of receiving DTB.
This emergency alert broadcast receiving method requires the user to keep a DTB receiving unit, as well as a display unit, of the mobile station turned on in order to obtain emergency information from DTB.
Keeping the DTB receiving unit and the display unit turned on irrespective of whether there is an emergency such as disaster or not increases power consumption of the mobile station. The mobile station accordingly has less standby time, talk time and data communication time.
To solve this problem, such a mobile station has been proposed that is always ready to receive emergency alert signals but not other signals and enters a state capable of receiving and displaying DTB when emergency alert signals are received, instead of maintaining the state of receiving and displaying DTB all the time. This type of mobile station keeps its DTB receiving unit turned on to receive broadcasts all the time while keeping its display unit turned off. The display unit is turned on when emergency alert signals are received, so that an emergency alert received through DTB is displayed on the mobile station.
This mobile station consumes less power than the above-described model which constantly receives and displays DTB. However, there is a problem in that the newer mobile station still wastes power since the DTB receiving unit is continuously kept turned on regardless of whether there is a disaster or not. Furthermore, the value of disaster information varies greatly depending on whether or not the person who receives the disaster information is affected by that particular disaster. That is, if the location of the disaster is near where the receiver is, the disaster information prompts the receiver to secure his/her personal safety whereas information on a disaster in a faraway place could just be information that has no bearing to the receiver. On the other hand, information on a disaster far from the receiver's current location may cause the receiver to check on his/her family's safety if the disaster is near his/her home. Thus, lack of proper power control with the location of a disaster taken into account lets the mobile station waste power in receiving information that may not be of any value to the user.
This problem is addressed in the following conventional art.
The Japanese Patent application Laid-open No. 2005-051602 discloses a digital broadcast receiver capable of sending a message to a preset emergency contact address upon receiving an emergency alert or the like. The emergency contact address is set in the digital broadcast receiver in advance and, when receiving a broadcast signal, the digital broadcast receiver detects an emergency alert signal or an entitlement management message (hereinafter abbreviated as EMM). The detected emergency alert signal or EMM is converted into an e-mail format and then sent to a server, which transfers the mail from the digital broadcast receiver to a communication terminal. A user carrying the communication terminal in a place away from the digital broadcast receiver can thus check the emergency alert signal or EMM.
However, this digital broadcast receiver too needs to maintain a state capable of receiving an emergency alert all the time even when there is no emergency, and does not have a function of reducing its usual power consumption.
The Japanese Patent application Laid-open No. 2005-117584 discloses a cell phone terminal with a television receiving function that can transfer the contents of a special newscast or the like to another registered cell phone terminal by e-mail without needing to make any functional changes to a broadcast station. The cell phone terminal first extracts a frequency component of an alarm sound from an audio signal outputted from a TV tuner unit, and determines whether or not the level of the extracted frequency component exceeds a preset threshold and matches a certain pattern. Next, the cell phone terminal determines whether or not a signal in scanning lines of a telop area, which is set in advance on a television screen, fits a white signal pattern indicative of emergency information. After recognizing from the decisions that emergency information has been received, the cell phone terminal controls the recording of the television screen and stores the recorded data in a memory. The recorded video data of the emergency information is attached toe-mail, which is then sent to an address registered in advance.
The cell phone terminal with a television receiving function too needs to maintain a state capable of receiving TV broadcasting all the time and does not have a function of reducing usual power consumption of a mobile station.
The Japanese Patent application Laid-open No. 2003-15311 discloses a cell phone that doubles as a DTB receiver and that has solved the problem of competition in MPEG-4 processing between the DTB mode and the cell phone mode. This cell phone has a function of receiving an emergency broadcast through DTB and a function of displaying contents of the emergency broadcast.
However, this cell phone too needs to maintain a state capable of receiving DTB all the time in order to catch an emergency broadcast, and does not have a function of reducing usual power consumption of a mobile station.
The Japanese Patent application Laid-open No. 2004-336227 discloses a mobile station and an emergency broadcast system that enable a user to view and listen to an emergency broadcast delivered in a television signal format in a notification form of his/her choice. The emergency broadcast system sends out an emergency broadcast composed of an announcement broadcast, which preannounces the start of an emergency broadcast, and an actual emergency broadcast, which follows the announcement broadcast. Formats in which the announcement broadcast is delivered include broadcasting by a television broadcast station and e-mail via a basestation for the mobile station. To receive the emergency broadcast, the mobile station is triggered by the reception of the announcement broadcast to prepare for a download of the emergency broadcast, which is transmitted after the announcement broadcast. Upon receiving the emergency broadcast, the mobile station outputs the contents of the received emergency broadcast in a given notification format.
The mobile station has to be always ready to receive the announcement broadcast and, in the case where the emergency broadcast systems ends the announcement broadcast as a television broadcast, the mobile station needs to maintain a state capable of receiving television broadcasting all the time even when there is no emergency. Thus, the mobile station constantly wastes power.
In the case where the emergency broadcast system sends the announcement broadcast by e-mail, on the other hand, the mobile station only has to be in a usual standby state, and accordingly consumes the minimum power.
However, in order to send the announcement broadcast by e-mail to the mobile station that needs to receive the emergency broadcast, a search has to be conducted first for the e-mail address of the mobile station that is in the broadcast area of the emergency broadcast. Then the announcement broadcast has to be sequentially sent by e-mail to every mobile station whose e-mail address has been retrieved by the search. Therefore, it takes long to complete sending the e-mail to every pertinent mobile station, and a total communication data amount is large. Furthermore, the contents of the emergency broadcast has to be converted into character strings or the like according to a given e-mail format, which makes it necessary for base stations and switching stations to have a function for accomplishing the conversion.
From another point of view, of the emergency broadcast system, which is to ensure the reception of the emergency broadcast by the mobile station, is sufficiently fulfilled by simply setting the mobile station to a state capable of receiving the emergency broadcast with the reception of the announcement broadcast as a trigger. Therefore, delivering information such as the contents of the emergency broadcast bye-mail is redundant, and it can be said that the emergency broadcast system is inefficient.